Blades and blade mounting assemblies for turbines and axial flow compressors



Jan. 3, 1.961 L. J. DENNIS 2,967,043

BLADES AND BLADE MOUNTING ASSEMBLIES FOR TURBINES AND AXIAL FLOWCOMPRESSORS Filed Nov. 12, 1957 2 Sheets-Sheet 1' (o m I4 0 If I!!! 4 IfI INVENTOE LEONARD J DENms,

ATTORNEY L. J- DENNIS BLADES AND BLADE-MOUNTING ASSEMBLIES FOR TURBINESAND AXIAL FLOW COMPRESSORS Filed NOV. 12, 1957 Jan. 3 11961 2Sheets-Sheet 2 INVENTOR LEONARD J. DENNIS ATTQRNEY" United States PatentBLADES AND BLADE MOUNTING ASSEMBLIES TURBINES AND AXIAL FLOW COMPRES-Leonard J. Dennis, Carpenders Park, England, assignor to D. Napier &Sons Limited, London, England, a British company Filed Nov. 12, 1957,Ser. No. 695,841

Claims priority, application Great Britain Nov. 30, 1956 4 Claims. (Cl.253--77) This invention relates to blades and blade mounting assembliesfor turbines or axial flow compressors, of the kind in which themounting is provided with a ring of substantially axial grooves toreceive the blade roots and each blade is made of sheet metal or tubemanipulated into hollow aerofoil form.

In practically all hollow blades manipulated from sheet metal or tubethere is a transition zone between the actual aerofoil zone and the rootzone that lies within the groove in the blade mounting. Since in thetransition zone the blade does not have the required aerodynamic form ofthe aerofoil zone it is a common practice to provide the blades withplatform members which abut between the blades. The platform membersafford a barrier between the transition zones and the flow channelsbetween the blades in the aerofoil zones. In conventional forms ofhollow blades the provision of a platform member on each bladecomplicates the construction of the blade and increases its weight,thereby increasing the centrifugal loading that has to be resisted bythe blade root in the case of a rotor blade.

In a blade and blade mounting assembly according to the presentinvention the mounting is provided with a ring of substantially axialgrooves to receive the blade roots, each blade is made of sheet metal ortube manipulated into hollow aerofoil form with two root tongues, onetongue extending from the concave flank and fitting in one of the saidgrooves in the mounting together with the root tongue extending from theconvex flank of the adjacent blade on one side, and the other tongueextending from the convex flank and fitting in the adjacent groovetogether with the root tongue extending from the concave flank of theadjacent blade on the other side, and there are platform members betweenadjacent blades each platform member having a projection which entersthe groove occupied by root tongues of the blades on each side of it.

This arrangement enables the root tongues to be spaced a substantialdistance apart to lend lateral rigidity to the blades while the groovescan be made relatively narrow, and it also permits the provision ofplatform members which are separate from the blades and which thereforedo not increase the weight or complicate the construction of the blades.

In one form of the invention each platform member is approximately T- orL-shaped in cross-section, the stem of the T or L constituting theprojection which enters the groove and the cross piece of the T or Lconstituting a barrier which extends between adjacent blades. In such anarrangement, the side walls of each groove may be undercut, the roottongues being formed to extend into these undercut portions of thegroove and the projection of the platform member having an enlarged andthe width of which is wider than the gap between the root tongues at themouth of the groove. Thus, in the case of a turbine or compressor rotor,centrifugal forces acting on the platform member cannot cause it to flyout of the groove since it will be retained therein by the enlarged endof the projection. Moreover, the projection will also help to retain theroot tongues of the blades in the groove.

If desired, a retaining key may be inserted into each groove to wedgethe two root tongues and the platform projection firmly in the groove.

At least one root tongue of each blade, in the transi tion zone betweenthe aerofoil zone and the root zone of the blade, may be provided with aresilient lug engaging an adjacent platform member and serving to modifythe vibration characteristics of the blade.

In another form of the invention a tubular ferrule extends transverselythrough each blade in the transition zone between the aerofoil zone andthe root zone, and at least one lacing wire passes through theseferrules and through the platform members, which wire serves to modifythe vibration characteristics of the blades. It is known that wirelacing has an advantageous effect on blade vibration characteristics,but it has hitherto been the customary practice to thread such lacingwires through the aerofoil portions of the blades. This has thedisadvantage that the lacing wires are in the gas stream. By putting thelacing wire in the transition zone it is removed from the gas stream.The ferrules reduce wear in the thin metal of the blades where thelacing wire passes through the blades, and in the wire itself.

One form of blade and blade mounting assembly embodying the invention,and two modifications thereof, will now be described by way of examplewith reference to the accompanying drawings in which:

Figure l is an exploded perspective view of a fragment of a turbinerotor embodying the invention, showing part of the turbine disc, twoadjacent turbine blades, a platform member shared by these two blades,and a retaining key for these parts;

Figure 2 is a fragmentary cross-section of the assembled turbine rotorof Figure l on a larger scale;

Figure 3 is a fragmentary cross-section similar to Figure 2 showing amodification;

Figure 4 is a fragmentary cross-section similar to Figure 2 showinganother modification; and

Figure 5 is a developed circumferential section taken on the line V-V inFigure 4.

Referring to Figures 1 and 2 of the drawings, the turbine rotor consistsof a turbine disc 10 having straight axial grooves 11 formed around itsperiphery. Each groove 11 is undercut so that in cross-section it has acircular inner portion 12 communicating with the periphery of theturbine disc through a relatively narrow mouth 13. Thus the side walls51, 52 of each groove 11 have undercut lower portions defined by saidcircular inner portion 12, and overhanging upper extremities 53, 54defining said mouth13.

Each blade is made of a single piece of sheet metal or tube manipulatedinto appropriate form, and consists of an aerofoil zone 14 having aconvex flank 15 and a concave flank 16, and, extending from the flanks,root tongues 17 and 18 respectively. Each root tongue comprises atransition zone 19 and terminates in a root zone 20. In the root zonethe extremities of the root tongues are shaped to fit in the grooves 11,one tongue 17 in one groove and the other tongue 18 in the adjacentgroove. The root tongues 17 and 18 are splayed outwardly so as toprovide a considerably wider base for the blade than is obtained inconventional constructions in which the root portion of a blade isreceived in one groove in the rotor.

Disposed between and shared by adjacent blades there are separateplatform members 21. Each platform member is approximately T-shaped incross-section for the major portion of its length, except at and nearits centre where it is approximately L-shaped as shown in Figure 2,

this change in section being due to the curved form of the top portionor cross-piece 55 of the platform mem her. This top portion has a convextop edge 22 and a concave top edge 23. The convex top edge 22 liesagainst the concave flank 16 of the blade on one side of the platformmember, at the level of the junction between the aerofoil zone 14 andthe transition zone 19, and the concave top edge 23 lies against theconvex flank 15 of the blade on the other side, also at the level of thejunction between the aerofoil and transition zones. A perforatedprojection 24 which constitutes the stem of the T or L in cross-sectionis straight to conform to the groove 11 in which it is to be inserted.The foot of the projection 24 is in the form of a semi-cylindrical bulgewhich lies within the circular undercut portion ,12 of the appropriategroove 11 in the assembled rotor,

with the extremities of the root tongues 17 and 18 which fit into thisgroove lying one on each side of it. The thickness of the projection 24above the bulge 25 is such that the projection will just pass throughthe gap between the root tongues 17 and 18 in the mouth 13 of the groove11 At the ends of the platform member 21 there are end walls 26 and 27respectively, which walls blank off the, ends of the spaces between theblades in the transition zone 1 Toassemble the rotor, the blades andplatform members are first assembled into a ring on a suitable jig andthe rotor disc is then applied in an axial direction so that the foot ofthe projection of each platform member and the adjacent root tongues ofthe blades on each side together enter one of the grooves in the rotor.Semicylindrical keys 28 are then driven into thesemi-cylindrical spacesleft in the grooves between the extremities of the root tongues thereinand beneath the bulges 25 of the platform members, so as firmly to wedgethe platform members and the root tongues in the grooves.

Referring now .to the modification shown in Figure 3, a resilient lug 30is welded to the root tongue 18 of each blade. Each lug is approximatelyL-shaped in crosssection, one limb 31 having a hole 32 in it throughwhich the weld metal 33 isapplied, and the other limb 34 being doubledover to press against the underside of the top of they adjacent platformmember 21. There is an aperture 35 in the bend between the two limbs ofthe lug,

to increase the resilience. of the lug. The limb 34 of the lug, byresiliently pressing against the platform member 21, provides frictionalrestraint against transverse vibrations of the blade and therebymodifies favourably thevibration characteristics of the blade.

Referring to the modification shown in Figures 4 and 5, a ferrule 37extends through apertures in the root tongues 17 and 18 of each bladeand is welded or brazed in position. The bore of. the ferrule is reducedatv 38 as shown in Figure 5, and, a lacing wire 39 is threadedcircumferentially through the bores of all the ferrules, this wire beinga snug fit in the reduced bores 38.. At intervals, in its length thewire 39 may be bulged as shown at 40 or otherwise deformed in order tolocate it circumferentially. The lacing wire passes through thetransition zone 19 of each blade and through one of the. perforations 41in the projection 24 of each platform member. The lacing wire-favourablymodifies the vibration characteristics of the blades by applyingfrictional restraint against lateral flutter. The ferrules prevent thelacing wire from causing wear on the root tongues where the wire passesthrough the latter.

Since the present invention permits wide spacing of 4 the root tongues17 and 18 of each blade, apertures such as 56 may be provided betweenthese tongues for the admission and/or discharge of cooling medium if itis desired to circulate this through the interior of the hollow blades.

What I claim as my invention and desire to secure by Letters Patent is:

l. A blade and blade mounting assembly comprising a plurality of bladeseach made of thin metal and having an aero'foil portion with 'a convexflank and a concave flank, a first root tongue extending from saidconvex flank and a second root tongue extending from said concave flank,said blade mounting having grooves therein including side walls defininga plurality of substantially axial blade root supports, said side wallshaving undercut lower portions and overhanging upper extremitiesdefining a mouth to each of said grooves, platform membersdisposedbetween adjacent blades, each platform member having a projectionreceived in one of said grooves which groove also receives said firstroot tongue of a blade adjacent one side of said platform member andsaid second root tongue of a blade adjacent the opposite side of saidplatform member, said first and second root tongues extending throughsaid mouth into said undercut lower portions and fitting against saidgroove side walls with a gap between said root tongues at said mouth,said projection of said platform member extending through said gap andhaving an enlarged inner end the width of which is wider than said gapand which fits between said first and second root tongues, and aretaining key in each groove engaging said projection beneath saidenlarged inner end and urging said projection toward said mouth to wedgesaid first and second root tongues between said enlarged inner endthereof and said overhanging upper extremities of said groove sidewalls.

2. A blade and blade mounting assembly according to claim 1 in whicheach platform member has a crosspiece constituting a transverse barrierextending from the convex flank of said blade on one side of said plat-;form member to the concave flank of said blade on the opposite side ofsaid platform member.

3. A blade and blade mounting assembly according to claim 1 in whicheach. root tongue has a root zone which lies within one of saidgroovesand a transition zone extending from said root zone to said aerofoilportion, and a resilient lug is provided on at least one root tongue ofeach blade in said transition zone which lug engages the adjacentplatform member.

4. A blade and blade mounting assembly according to claim 1 in whicheach root tongue has a root zone which lies within one of said groovesand a transition zone extending from said root zone to said aerofoilportion, a tubular ferrule extends transversely through the two roottongues of each blade in said transition zone, and at least'one lacingwire extends through said ferrules and said platform members.

References Cited in the file of this patent FOREIGN PATENTS 15,893 GreatBritain 1903 59,398 France Jan. 6, 1954 (1st addition to 969,413)

. 131,574 Australia Mar. 1, 1949 701,263 Great Britain Dec. 23, 1953998,221 France e Sept. 19, 1951

